In a conventional art, an indicating part in a display instrument is lighted so that the indicating part is visible even in a state where light from the outside is weak. The conventional art includes, for example, a display instrument for a vehicle disclosed in JP-A-2004-345590 (hereafter, referred to as a patent document No. 1). The display instrument for a vehicle includes a plurality of light-emitting diodes and an LED circuit. The light-emitting diodes light an indicating part. The LED circuit is coupled with a power source and applies a driving current for activating the light-emitting diodes to the light-emitting diodes. The display instrument further includes a transistor coupled with the LED circuit and a switch control circuit that controls supply of the driving current to the light-emitting diodes by the transistor.
In the display instrument, the switch control circuit can apply the driving current from the power source to the light-emitting diodes by controlling the transistor. Accordingly, the light-emitting diodes emit light.
A configuration of an indicating part in a display instrument is increasingly complicated. The number of light-emitting diodes for lighting the indicating part increases with an increasingly complicated indicating part. The number of LED circuits and the transistors for activating a large number of light-emitting diodes also increase. Thus, a configuration of a lighting device is increasingly complicated.
In some lighting device, light-emitting diodes need to emit light alternately. However, in the configuration described in the patent document No. 1, the light-emitting diodes are activated or deactivated simultaneously when the switch control circuit controls each of the transistors. Thus, the configuration described in the patent document No. 1 may activate the light-emitting diodes inappropriately.